The present invention relates to a gas bag module.
Known gas bag modules comprise a gas bag with a gas bag wall which has a front and a rear wall section, a depression including a mouth and running in the inflated state from the front wall section to the rear wall section. The depression is formed in that a part of the gas bag wall is prevented from an unimpeded movement away from the module on unfolding. Such gas bags are intended to be incorporated in the steering wheel or the instrument panel and to protect the occupant during a frontal impact. The gas bag has an annular chamber which is to be inflated, the inner wall, delimiting the depression, being formed by the depression. The depression extends from the front wall centrally towards the rear, and the lowest point of the depression is formed by a fabric piece which is permanently fastened to the gas bag module and hence on unfolding is not moved towards the occupant. Furthermore, the gas bag usually emerges obliquely outwards from the module owing to the annular shape of the chamber, and only subsequently does the front wall section move in the direction toward the occupant.
With an occupant sitting centrally and in the presence of a high impact intensity, it must be prevented that the occupant""s head can plunge into the depression.
The invention provides a gas bag module in which the gas bag even with an occupant sitting centrally and with a high impact intensity achieves excellent restraint values. This is achieved in a gas bag module which comprises a gas bag with a gas bag wall which has a front and a rear wall section. A depression is provided which has a mouth and runs in an inflated state of the gas bag from the front wall section to the rear wall section, which depression is formed in that a part of the gas bag wall is prevented from an unimpeded movement away from the module on unfolding of the gas bag. The module further comprises at least one closure piece which is fastened to the gas bag wall such that in the inflated state it moves in front of the mouth of the depression and closes the depression. The mouth of the depression is the transition of the front wall section to the depression, i.e. the inlet thereof. The closure part moves in front of this inlet, so that at the end of the inflation process a closed wall, without accessible depression, is available to restrain the occupant. The depression is not a chamber to be filled by the gas of the gas generator and is not in flow connection with the gas generator.
According to one embodiment, the closure piece is a fabric piece which is sewn to the gas bag wall.
This closure piece can be constructed in a band shape, the two ends of the band being able to be fastened to the rear wall section, and the band running across the front wall section. The band is simple to fasten, is flexible and does not represent a projecting part. The displacement of the band takes place by the front and rear wall sections moving relative to each other, without a device, to be actuated separately, being required for the displacement of the band.
A closure piece constructed in a cross shape, which is fastened by the free ends on the rear wall section, also offers similar advantages. The crossing point then closes the depression. Through the cross-shaped form, a higher stability of the closure piece is produced compared with the embodiment with a band-shaped closure piece.
Another design makes provision that at least two closure pieces are provided. These closure pieces are preferably connected with each other, the connection allowing a relative movement of both closure pieces with respect to each other. This has the advantage that in the folded state they can be laid around a central holding piece which will be explained in further detail below. In the unfolded state, the two closure pieces, which preferably overlap each other, safely close the depression and fix each other in their relative position.
One closure piece may, for example, have at least one leadthrough opening for the other closure piece, the latter extending right through the leadthrough opening and preferably as far as into the depression.
In this arrangement, a band-shaped prolongation of one closure piece may extend through the leadthrough opening and as far as to a central holding piece to which also the one part of the gas bag wall is fastened that is prevented from an unhindered movement towards outside of said module. The band-shaped prolongation fastened to the holding piece acts as a limiting strap here.
The, for instance, band-shaped or cross-shaped closure pieces can help also to replace the limiting straps which were usual hitherto, which delimit the movement of the front wall section and are intended to give the gas bag a defined shape. The holding back of the gas bag wall can in fact take place or be supported by the band-shaped or cross-shaped closure piece.
The gas bag is preferably housed in an annular chamber in the gas bag module which is defined on the inner face by a centrally arranged holding piece. This holding piece serves mostly to prevent a central piece of a covering of the module from moving outwards. The holding piece extends in the folded state of the gas bag inside the depression, with the depression moving along the holding piece on unfolding and leaving the module via an annular outlet opening. The closure piece, in the folded state, is placed around the holding piece and can then move on inflation such that it comes to lie in front of the depression.
Another embodiment makes provision that the closure piece has an opening through which, in the folded state, the holding piece extends. On unfolding, the opening moves, more precisely the edge of the opening, outwards along the holding piece. On inflation, the displacement of the closure piece then occurs relative to the gas bag wall, so that the opening is situated outside the depression in the fully inflated state. The embodiment with an opening has the advantage that the closure piece can be constructed as a fabric section having a large area and covering the entire front wall section like a second skin.